北太平洋副热带逆流区涡旋动能谱的季节性变化及其机制

摘要

本文利用了23年的卫星高度计数据和WOA13气候态月平均温盐资料,考察了北太平洋副热带逆流(STCC)区涡旋动能谱及其涡旋尺度季节变化的动力过程.为了揭示其动力机制,本文采用了斜压2.5层模式并结合动能串级的理论进行分析.结果表明,在STCC区由于海洋层结及地转流的垂向剪切发生了季节性变化,从而产生的斜压不稳定是导致涡旋动能谱季节变化的原因.涡旋动能最大的时间发生在5-6月份,滞后于斜压最不稳定发生的时间(3月份)约2-3个月左右,这是由于斜压不稳定产生的扰动需要一定时间才能发展成振幅足够大的涡旋.斜压不稳定提供的能量使得涡旋相互作用加强,产生了动能逆向串级,动能谱向更大尺度转移.涡旋能量尺度在3月份仅为280km,而在9月份达到最高值335km左右.另一方面,我们发现STCC区动能谱斜率及动能谱通量也有季节变化,在涡旋动能最大的5-6月份,当尺度小于罗斯贝变形尺度时,谱斜率达到lk-3而动能谱通量达到最大值.对STCC区涡动能谱及涡旋尺度季节变化的研究,对深入认识中尺度涡旋的产生及其演变机制有着重要的意义.%Seasonal variation in eddy kinetic energy spectrum in the North Pacific Subtropical Countercurrent (STCC) was investigated based on 23-year satellite altimeter data and WOA2013 climatological monthly mean temperature and salinity data.To reveal the mechanism of the seasonal variation of the spectrum and the eddy scale in the STCC region,the baroclinic 2.5-layer model and kinetic energy cascade theory was used.The results show that baroclinic instability that resulted from seasonal shear and stratification in STCC-NEC (North Equatorial Current) is the cause of the seasonal variation in eddy the kinetic energy spectrum.The maximum eddy kinetic energy occurs in May-June,lagging for 2-3 months behind the baroclinic instability peak (March),as the initial perturbation of baroclinic instability takes time to grow into finite-amplitude eddies.The energy from the baroclinic instability intensifies the eddy interaction,and produces a reversal cascade of kinetic energy,making eddy kinetic energy a spectral shift to a larger length scale.In March,the energy containing length scale reaches minimum about 280km,and maximum of about 335km in September.In addition,we found that the slope of kinetic energy spectrum and the kinetic energy spectrum flux vary in season,too.The kinetic energy spectrum reaches the maximum in May-June.When the scale is smaller than the Rossby deformation,the power spectrum slope is 1k 3 and the kinetic energy spectrum flux grows to maximum.Therefore,it is practical to study the mechanism of mesoscale vortex generation and its interaction by studying the seasonal variation of eddy energy spectrum and eddy scale in STCC region.